Infectious diseases of bacterial origin have made a dramatic comeback, highlighting the urgency to develop new therapeutic tools. However, a better understanding of host-pathogen interaction at the cellular and molecular level is needed to define new targets. Our long-term goal is to develop such new therapeutic tools. Different pathogens use a variety of molecular machineries to penetrate host cells and manipulate intracellular vesicular trafficking. For instance, viruses employ glycoproteins, which are structurally and functionally similar to the SNARE proteins that mediate eukaryotic membrane fusion and vesicular trafficking. Large scale sequencing of bacterial genomes has revealed that many bacteria also express membrane proteins with homology to the eukaryotic SNARE fusion machinery components. These SNARE-like proteins might share similar functions and could be used by microorganisms to either block or promote membrane fusion. This project will test the hypothesis that bacterial SNARE-like proteins interact with the eukaryotic SNAREs to manipulate membrane fusion to their advantage. First, we will explore the interaction between bacterial SNARE-like proteins and mammalian SNAREs, using two Chlamydia and two Legionella SNARE-like proteins as our models. Next, we will assess the effect of bacterial SNARE-like proteins on mammalian SNARE- mediated membrane fusion. Finally, we will identify and characterize the functions of the bacterial SNARE-like protein bioactive domains. The presence of SNARE-like proteins in different pathogenic organisms indicates that the SNARE motif may have been selected during evolution because it is an efficient structural motif for manipulating eukaryotic membrane fusion and thus contribute to pathogen survival. Such a recurrence would allow us to develop a common strategy for targeting a wide array of bacterial SNARE-like proteins. Designing new bacterial therapeutics capable of corrupting the bacterial SNARE-like domains should revert the blockage of fusion and allow bacteria clearance by the phagosomes. PUBLIC HEALTH RELEVANCE: This research project proposes to determine whether intracellular bacteria utilize SNARE-like proteins to manipulate host vesicular trafficking pathways. Results will contribute to a better understanding of how parasite-containing vacuoles bypass lysosomal degradation and will shed light on the mechanism of parasitic intracellular survival. Additionally, the proposed studies have practical applications for the development of new therapeutic approaches to induce the clearance of intracellular bacteria by the host cell.